Some print apparatus disperse print materials such as coloring agent, for example comprising a dye or colorant, from a printhead. An example printhead includes a set of nozzles and a mechanism for ejecting a selected agent as a fluid, for example a liquid, through a nozzle. In such examples, a drop detector may be used to detect whether drops are being ejected from individual nozzles of a printhead. For example, a drop detector may be used to determine whether any of the nozzles are clogged and would benefit from cleaning or having some other maintenance operation performed thereon.